Do so – even tentatively – and progress never feels anything less than extraordinarily brisk. But it’s never brusque, and that’s the magic of this saloon. From 3000rpm, the torque of the engine propels a 1950kg chassis like a leaf in the wind, and while nobody ever needed this much power, its latency is omnipresent and that’s a warming sensation.
This engine is also less reliant on synthesised tones than its M division cousin, and a muted but sweet thrum is well in keeping with Alpina’s discreet persona. Some might consider the big-bore brace of double-barrelled exhaust tips to be slightly misleading and maybe the timbre could do with just a little more bite. Personal taste and all that.
But what of the ride? There’s usually a suspicion with Alpina cars that road noise and the intrusiveness of ripples, potholes and so forth could be mitigated that bit more if only the hallmark multi-spoke alloy wheels were just a fraction smaller, but here that’s not the case.
The broad dynamic repertoire of the adaptive dampers and the B5’s new suspension kinematics somehow find a way to breathe in time with almost any stretch of Tarmac, and you would have to be travelling at a rate far above the legal limit to catch this chassis falling a step behind the topography.
So undemanding of its driver is the B5 that you don’t automatically appreciate the level of mechanical finesse, with the car working its custom Pirelli P Zero rubber much harder than it ever lets on. Its natural gait seems to be at seven or eight-tenths, at which point the ride is superbly cushioned and body movements quickly but deftly controlled.
Beyond that, there’s an element of float in the suspension and the body has a tendency to pogo, but by then you’ve rather missed the point.
As luck – or fastidious engineering, perhaps – would have it, you needn’t push particularly hard to enjoy the neutral balance of this chassis, not least because Alpina’s recalibration of the M550i’s rack means that it feels natural to place the B5 precisely where you would like it. The roll rate is also gloriously judged and compels you to lean on the front, set the rear and then drive through a corner with such purpose it’s as though it were your calling in life.
For £2500, Alpina will also fit a mechanical limited-slip differential hand-built by Drexler, and you’d be wise to tick that box. With such a massive contact patch, there are deep reserves of grip, but gently overload the chassis through a suitable parabolic bend and the B5 feels light on its feet, eventually pushing through only a veneer of understeer before the rear axle starts to swing into an effortless and controllable slide.
Such behaviour is peripheral to the B5’s true purpose; that it will nonetheless indulge its driver so wholeheartedly is testament to this car’s incredible breadth.
One more thing: our car’s high-performance brakes system – a £1400 option that adds lightweight composite discs – felt intuitive for stops both heavy and light, although Alpina warns that it can be noisy compared with the standard cast-iron set-up (not that we noticed). For a relatively modest additional outlay, it’s worth having.